Field of the Invention
The present invention relates to a sheet processing apparatus, a method of controlling the same, and a storage medium.
Description of the Related Art
In conventional sheet processing apparatuses, during production of saddle-stitched books, a folding position for center-fold processing is sometimes displaced from the center of a sheet. The displacement of the folding position from the middle of a sheet is caused e.g. by an assembly error of a sheet processing apparatus, variation in sheets between production lots of the sheets, and a change in sheets due to changes in environmental conditions, such as humidity and temperature.
To cope with this, conventionally, several copies are printed for test printing before final production of saddle-stitched books so as to check whether or not a folding position is at an expected position. Then, if the folding position is displaced from the expected position, fine adjustment is performed physically or by software such that the folding position is arranged at the expected position.
In relation to this, there has been proposed a sheet processing apparatus that is capable of correcting displacement of a folding position within approximately ±1 mm, by providing two setting items for adjusting the folding position and the stitched position such that they are accurately arranged in the middle of each sheet during production of saddle-stitched books (see e.g. Japanese Patent Laid-Open Publication No. 2001-206626).
The two setting items are an item which can be set only by a service technician for correcting the above-mentioned displacement due to an assembly error, and an item which can be set by a user for correcting displacement due to a sheet.
This makes it possible to prevent the position on which saddle-stitch processing and center-fold processing are performed from being displaced from the middle of a sheet.
For production of saddle-stitched books, in some cases, processing operations up to center-fold processing are performed by a sheet processing apparatus, and subsequent processing operations including saddle-stitch processing are performed using another sheet processing apparatus (off-line apparatus) which is different from the above-mentioned sheet processing apparatus. Further, the off-line apparatuses include one configured to feed sheets one by one by pinching an extending portion (portion of a sheet, which does not overlap when being folded) of an end of a sheet with rollers. In the off-line apparatus of this type, if a sheet is folded in the middle, an extending portion of an end of the sheet is not generated, and as a result, the off-line apparatus cannot accurately feed the sheet (fold section, i.e. signature).
A production method in which saddle-stitch processing and processing steps thereafter are performed using an off-line apparatus is generally determined from the viewpoint of productivity, based on related factors, such as a difference in the number of sheets which can be bound, a level of the accuracy of binding, and a level of speed at which the off-line apparatus can perform processing.
When producing saddle-stitched books using the above-mentioned production method, a print product generated by the sheet processing apparatus is required to have a center-folding position shifted from the center of a sheet by a predetermined length.
The sheet processing apparatus disclosed in Japanese Patent Laid-Open Publication No. 2001-206626 is capable of performing fine adjustment for correcting the displacement of a folding position from the center of a sheet, caused by the above-mentioned assembly error, and displacement of a folding position from the center of a sheet, caused by the above-mentioned variation in sheets.
On the other hand, the sheet processing apparatus disclosed in Japanese Patent Laid-Open Publication No. 2001-206626 does not take into consideration shifting of a folding position from the center of a sheet, and further, is not capable of performing adjustment large enough to create a fold section, a fore edge of which is generally required to have a length of 5 mm to 10 mm, demanded by the above-mentioned production method.
Further, when shifting a folding position from the center of a sheet, it is necessary to adjust the position of an image to be printed on the sheet in accordance with the adjustment of the folding position. In the sheet processing apparatus disclosed in Japanese Patent Laid-Open Publication No. 2001-206626, however, the image position adjustment is not taken into consideration.